package: use SPDX short identifier for GPLv1/GPLv1+

package: use SPDX short identifier for GPLv1/GPLv1+

We want to use SPDX identifier for licenses as much as possible. SPDX
short identifier for GPLv1/GPLv1+ is GPL-1.0/GPL-1.0+.

This change is done using following command.
find . -name "*.mk" | xargs sed -ri '/LICENSE( )?[\+:]?=/s/GPLv1(\+)?/GPL-1.0\1/g'

Signed-off-by: Rahul Bedarkar <rahulbedarkar89@gmail.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>